Grease composition

ABSTRACT

GREASE CONSISTING OF PERFLUOROALKYLPOLYETHER BASE OIL THICKENED WITH POLYTETRAFLUOROETHYLENE AND CONTAINING MINOR AMOUNTS OF BORON NITRIDE AND TUNGSTEN DISULFIDE.

United States Patent 01 ice 3,801,505 Patented Apr. 2, 1974 3,801,505 GREASE COMPOSITION Van Y. S. Hong, Rock Island, 111., assignor to the United States of America as represented by the Secretary of the Army No Drawing. Filed July 25, 1972, Ser. No. 275,025 Int. Cl. Cm 7/18, 7/28 US. Cl. 252-25 2 Claims ABSTRACT OF THE DISCLOSURE Grease consising of perfluoroalkylpolyether base oil thickened with polytetrafluoroethylene and containing minor amounts of boron nitride and tungsten disulfide.

The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to a high temperature lubricant and more particularly to a material for utilization as a lubricant at elevated temperatures, high load and speed, under various environmental conditions.

Certain weapon systems, e.g., the XM140 automatic gun developed by Philco-Ford Corporation, are operated at high speeds thereby generating high temperatures. This weapon comprises a lubrication system possessing the elements of supply, distribution, retention, and lubrication. This system is passive in character and consists of two reservoirs which hold sutficient material to supply lubrication for about 10,000 rounds of firing. The lubricator pad reservoir supplies a fluid lubricant to the barrel lock lubricator and lubricator pads by means of wicki'ng. The second reservoir supplies a grease lubricant to the drum cam path and cam follower assembly. The above components of the system are difilcult to lubricate due to the high temperatures and loads generated.

It is an object of the present invention to provide and disclose metallic surface lubricants effective in inhibiting wear or galling at elevated temperature gradients up to about 1500 F.

It is a further object of the present invention to provide and disclose metallic surface lubricants effective in inhibiting wear or galling at elevated temperatures under high loads.

Other objects and a fuller understanding of the invention may be ascertained from the following description and claims.

C o m m e r c i a l l y available perfluoroalkylpolyether (PFPE), having a molecular weight of about 7500, which is sold under the trademark of Krytox by E. I. du Pont de Nemours and Co., has been found to be an effective liquid lubricant for utilization in the lubricator pad reservoir of the XM140 automatic gun. While (PFPE) performed satisfactorily, it decomposes at temperatures of around 670880 F. Accordingly, a solid lubricant was developed consisting of perfluoroalkylpolyether in combination with a fluorinated olefin for lubrication of components attaining higher temperatures. Additives, i.e., boron nitride and tungsten disulfide were added to the base material. The boron nitride raises the decomposition temperature of the lubricant. The tungsten disulfide imparts stability to the material. Both materials serve as synergistic agents as well as lubricity agents at higher temperatures. Set forth in Examples 1 and 2 below are examples of lubricants prepared in accordance with the present invention.

The base grease consisted of a mixture of parts (PFPE) and 15 parts fluoroethylene telomer per parts of mixture. A range of 85-88 parts (PFPE) and 12- '15 parts fluoroethylene telomer was found operable. Commercially available fluoroethylene having a molecular weight of around 25,000, which is sold under the trademark of Vydax-l000 by E. I. du Pont de Nemours and Co., was utilized. Production of a homogenous mixture was obtained by conventional techniques. The boron nitride and tungsten disulfide had a particle size of about one micron. Operable ranges of the composition include about: 80.0 to 85.0% base grease; 8.0 to 12.0% (PFPE); 2.0 to 6.0% boron nitride; and 4.0 to 12.0% tungsten disulfide.

The grease lubricant of Example 1 was performance tested in the XM automatic gun in combination with liquid lubricant (PFPE). The liquid (PFPE) was utilized to lubricate the barrel lock lubricator pads and lock collar of the system. During the firing, the temperature of the lubrcated path of the cam and cam follower assembly of the gun system exceeded 1400 F. with the loads of 80,000 psi and velocities of 1000 feet per minute. The XM140 gun was successfully fired for over 60,000 rounds Without signs of wear or galling to the system.

The polytetrafluoroethylene utilized (TL-126) is commercially available from Liquid Nitrogen Processing Corporation of Malvern, Pa. Operable ranges of the above components include about: 60 to 62% (PFPE); 30 to 32% polytetrafluoroethylene; 2 to 6% boron nitride; and 4 to 12% tungsten disulfide. The polytetrafluoroethylene had a particle size of 8 to 10 microns. The boron nitride and tungsten disulfide had a particle size of about one micron. [while the material of Example 2 has not been performance tested in conjunction with the XM140 automatic gun, it is considered to be an effective solid lubricant based on laboratory evaluations. Set forth in the tables below is a comparison of the material of Example 2 with the material of performance tested Example 1.

TABLE Test evaluation 1 2 1. Evaporation, FTMS, 791 to 551, wt. percent at- 400 F. for 22 hrs 500 F. for 22 hrs 2. Flammability at 1,500 F. (2 to 3 gram sam l 3. Residue at 1,500 E, wt. percent 4. Penetration at 65 F., mm./10 per ASTM (modified) 5. Wear test: Shell 4-ball wear test at 40 kg, 1,200 r.p.m.,

168 F., 1 hr. avg. wear (mm.) 6. Change in consistency from elevated temperature to cool down to ambient:

a. Penetration at 77 F. before test, mm./10 b. Penetration at 77 F. after test, mm./10

1 Flame duration of not more than 30 see, flame not over 2 inches.

The amounts and proportions of components of the present solid lubricants are critical when used in conjunction with the XM14-0 automatic gun. For example, too large an increase or decrease in consistency as affected by various concentrations of additives or base oil would affect the degree of firmness of the grease. Any higher or lower consistency would affect the amount of grease ejected from the reservoir per ejection. Since the reservoir was specified to hold enough grease to last 10,000 rounds per each relubrication cycle, any deviation would affect the reliability of the weapon. If the con- 3 sistency of the grease is increased by 10%, this would cause greater amounts of grease to be depleted and, instead of lasting 10,000 rounds, the reservoir may be depleted, e.g., at the end of 8,000 rounds. Lack of lubrication in the remaining 2,000 would cause the weapon to become malfunctional.

In addition, too high a concentration of boron nitride or tungsten disulfide would leave excessive powder at channels and vents in the skate and cam follower assembly of the system. This would clog the channels and prevent passage of continuous lubricant to high temperature lubricating sites of the roller, roller bearing, etc.

Although the present lubricants have been described as having utility in an automatic gun assembly, it is obvious that the present lubricants may be utilized in any system requiring a lubricant resistant to elevated temperatures, high load, and performance.

Having described my invention, I claim:

1. A grease composition effective at temperatures exceeding 1400 F. and having a worked penetration in the range of 200 to 300, consisting essentially of the following components in percent by weight as indicated:

Percent Perfluoroalkylpolyether (M.W. about 7,500) 7 686.8 Polytetrafluoroethylene (M.W. about 25,000) 9.6-12.75 Boron nitride 2-6 Tungsten disulfide 4-12 Percent Perfluoroalkylpolyether 80 P'olytetrafluoroethylene l2 Boron nitride 4 Tungsten disulfide 4 References Cited UNITED STATES PATENTS 3,213,024 10/1965 Blake et al. 252-12 3,250,808 5/1966 Moore et a1. 252--12 3,505,229 4/1970 Skehan 252 54 3,525,690 8/ 1970 Christian 252--25 3,658,709 4/ 1972 Christian 25254 3,691,074 9/1972 Messina et a1. 25225 3,723,317 3/1973 Ulery 252-54 20 DANIEL E. WYMAN, Primary Examiner I. VAUGHN, Assistant Examiner US. Cl. X.R. 

